Synthesis of DilantinIntroductionDilantin is a well-known anticonvulsant used for the treatment of epilepsy. Dilantin is also used to treat syndrome of defects including craniofacial abnormalities, cardiac and limb defects, general deficiencies in growth and mental retardation5. However its pharmaceutical function is most popular for treatment of epilepsy. Epilepsy is a neurological disorder affecting about 1% of the population.1 It is known to be caused by uncontrolled firing of neurons that induce violent spastic movements.3 In order to seize the seizure attack, the drug must reach the synaptic receptors in the central nervous system.1 Unfortunately, many drugs are incapable of crossing over the blood-brain barrier due to their physical shape and chemical properties.1

Figure 1 Synthesis of DilantinIn 1938, dilantin (phenytoin) was discovered as a compound that controls epileptic convulsions. Dilantin distinguished itself from other drugs for its minimized side effects, such as not acting as a sedative, and not impairing consciousness, unlike previous phenobarbital anticonvulsant drugs.3 In addition to the minimal side effects, several reports indicate that unlike other anticonvulsant drugs, dilantin consists of neuro-protective and cardio-protective properties as well. Currently dilantin is one of the most widely used drug in the treatment of generalized tonic-clonic seizures and focal motor seizures.2 This pharmaceutical can be synthesized by a condensation reaction of benzene and urea and involves a benzylic rearrangement step. Condensation reactions take place between two carbonyl molecules and involve a combination of nucleophilic addition and alpha substitution steps. Normally, one of the carbonyls is converted into an enolate-ion nucleophile and adds to the electrophile carbonyl group of the other carbonyl. Thus, the nucleophilic molecule will undergo an alpha substitution reaction and the electrophilic molecule will undergo a nucleophilic addition.4 When benzyl and urea are heated together in a basic condition as a catalyst, they will condense to form dilantin. Then, an additional process is involved to rearrange both phenyls on the same carbon atom.3

Figure 2 Mechanism of DilantinOn the first step, the base attacks an amide proton (Urea) then the electron pushes through to make a double bond between carbon and nitrogen and negatively charged oxygen. Next, the nucleophilic carbon on the Urea attacks one of the electrophilic carbonyl groups of benzyl. The oxygen of the carbonyl group becomes negatively charged and attracts a proton to form an alcohol. Another nucleophile deprotonates an amide group, and the negatively charged nitrogen makes an additional bond with the adjacent carbon, thus producing a negatively charged oxygen. The electron from the oxygen pushes through to kick out the alcohol group, which produces a set up for the condensation intermediate that is similar to the aldol condensation.3 Once again, the similar step occurs on the other amide group. However this time, electron from the oxygen pushes through to create a five membered ring by attacking the electrophilic carbonyl group. When the negatively charged oxygens electron pushes through once more, the attached phenyl group migrates to produce the Dilantin skeleton.3 With a work up of protonation, this produces dilantin. The rearrangement of phenyl group is also known as the benzilic acid rearrangement, however the reason for this specific rearrangement is not clear. It is hypothesized that the stability of the imide (-CO-NH-CO-) group derives such arrangement.3 For this lab, Dilantin or phenytoin will be synthesized via a condensation reaction between benzyl and urea, which involves benzylic rearrangement step. The reaction will be monitored by TLC, and the crude product will be purified via recrystallization. The purity of the synthesized product will be analyzed by measuring the melting point, obtaining 60mHz 1H NMR data, 400mHz 1H NMR, 400mHz 13 C NMR, and IR data.

ExperimentDilantin (Phenytek). In a round bottom flask, Benzil (0.4g, 0.00190mmol), Absolute Ethanol (6ml, 0.130mmol), 30% (water/volume) aqueous solution of Sodium hydroxide (1.5ml, 0.0375mmol), and Urea (0.2g, 0.00333mmol) were mixed together in a reflux condenser. The reaction was monitored by TLC. The mobile phase was prepared with 50:50 Ethyl Acetate and Petroleum Ether. When the reaction was complete, it was added into cold distilled water (10ml, 0.556mmol), and the solution was acidified using glacial acetic acid (drop-wise). The precipitation was collected via vacuum filtration and dried. The dried crude product is purified through recrystallization in 95% Ethanol solvent. Crystals of Dilantin (0.008g, 1.67%) were collected by vacuum filtration. mp 292-294C; 1H NMR (60MHz, DMSO) (ppm) 7.732 (s, 4H), 7.370 (s, 4H), 7.060 (s, 10H); 1H NMR (400MHz, DMSO) (ppm) 11.1964, 9.3963, 7.4112, 7.4004, 7.3635, 7.3539, 7.3422, 7.3304, 3.5098, 2.5119; 13C NMR (400MHz, DMSO) (ppm) 174.7817, 155.9729, 139.8275, 128.4338, 127.9619, 126.5162, 70.1653, 39.9319, 39.7231, 39.5148, 39.3059, 39.0917, 38.8886, 38.6795; IR (ATR) max (cm-1) 3219.14, 1669.93, 1488.95, 1448.01.

Results and DiscussionDilantin was synthesized by reflux condensation reaction of Urea and Benzil, which were mixed together with ethanol and sodium hydroxide. The reaction was monitored via TLC, and the solution was added into cold distilled water with drops of glacial acetic acid. The precipitate was dried and was purified through recrystallization in ethanol solvent. The TLC was used to monitor the rate of the reaction. The reaction was compared with diluted benzil solution, the starting material, and the mobile phase was a 50:50 mixture of Ethyl Acetate and Petroleum Ether. This particular mobile phase was used to increase the Rf value of the diluted benzil solution, which normally has a very low Rf value due to its strong polarity. The reaction was stopped when the reaction solution no longer indicated the presence of the starting material; the reflux condensation was stopped when the reaction solution did not have the same Rf value of the diluted benzil solution under the UV light. The percent yield of the crude product was 104%, and the recrystallized product was only about 1.67% yield. The percent yield of crude product was over 100%, which indicates some impurities were present in the crude product. However, the very low percent yield of recrystallized product could have resulted due to adding too much solvent, 95% ethanol, for the solute to dissolve. The goal for heating the mixture is to create a saturated solution with minimum amount of solvent. If too much solvent was added, it will cause problems when trying to collect the crystals. Too much solvent will hold more solid on cooling and it may not crystallize. In fact, the recrystallization rate was very slow for my product, which explains the low yield of recrystallized product. To determine the structure and the purity of the synthesized product, melting point, IR, and NMR data were analyzed accordingly. To determine the purity of the synthesized product, melting point of the product can be compared with the melting point of the pure substance. The melting point of the pure Dilantin is 293-295C.6 The collected melting point was 292-294C, which is very close to the pure substance. This result highly suggests that the synthesized Dilantin has an identical melting point property with the pure compound. To further investigate the purity of the compound, IR data was collected. IR has been used to analyze the functional groups of the synthesized product and also to check the purity of the synthesized product. From the data, the peak at 3219.14 cm-1 indicates the presence of secondary amine group, and the strongest peak at 1669.93 cm-1 represents the presence of secondary amide group. Finally, peaks at 1488.95 cm-1 and 1448.01 cm-1 indicate the presence of benzyl ring group. From this IR data, the most important peaks that distinguish itself from the starting material, Benzil, are peaks at 3219.14 cm-1 and at 1669.93 cm-1. These two peaks indicate the presence of secondary amine group and secondary amide group accordingly. In fact Dilantin has two types of secondary amine groups and two types of secondary amide groups as well, where benzil only has two ketones and two aromatic benzyl rings attached on the side of the chain. Observing from the collected IR data, there is no significant peak that indicates the impurity of the synthesized product; for instance, no strong peak that indicates the presence of the starting material benzil can be found in the IR data.To further analyze the structure of the synthesized product of Dilantin, three different NMR data have been collected: 1H 60MHz NMR, 1H 400MHz NMR, and 13C 400MHz NMR. Three peaks at 7.060 ppm, 7.370 ppm, and 7.732 ppm are relevant to the hydrogens found in two benzyl rings. Since two benzyl rings are branched out from the same carbon, total ten hydrogens can be divided into three different groups. Thus, it is correct to see three distinct peaks around 6.5-8.0 ppm. The sum of the integrations under these three peaks should be close to ten, since ten hydrogens are present in these two aromatic benzyl rings. Specifically, one peak should have a triplet peak with integration of two hydrogens, and the other two should have two distinct doublet peaks with integration of four hydrogens under each peak. The remaining two hydrogens should be observed around 5.0-9.0 ppm, region where hydrogens attached to the amine group are normally found. Since Dilantin has two hydrogens attached to two different amine groups, two separated peaks should be observed around 5.0-9.0 ppm or perhaps a little higher shift value. However, no peaks around 5.0-9.0 ppm or a little higher than this value can be found on the collected 1H 60MHz NMR data. Usually amine groups will not appear clearly if not enough sample was in the NMR tube. Generally with higher resolution, like using 400MHz NMR, an ambiguous peak and small peaks that were ambiguous under 60MHz NMR will show up. For a better resolution of the NMR data, 1H 400MHz NMR data and 13C 400MHz NMR data were collected. Fortunately, two small single peaks at 11.1964 ppm and 9.3963 ppm were observed under 1H 400MHz NMR data. These two peaks strongly suggest the presence of hydrogen attached to the secondary amine group. Both peaks have integration of one hydrogen. And a cluster of peaks at 7.3304-7.4112 ppm with integration value of ten hydrogens indicate the presence of aromatic benzyl ring in the sample. A multiplet peak at 2.475-2.506 with approximately 3 hydrogens and another peak at 3.407 are present due to the solvent DMSO and water. Since dilantin is less likely to dissolve in d-Chloroform, using DMSO as a solvent for NMR was appropriate for a better result. The presence of water can be observed, if the NMR tube was not dried enough after cleansing it with acetone and water. Analyzing 13C 400MHz NMR data is very similar with analyzing 1H NMR. In Dilantin there are total seven distinct carbons in the molecule out of total fifteen carbons. The total peaks on the data are total seven, disregarding the multiplet peaks at 38.6795-39.9319 ppm. The multiple peaks at the range around 39 ppm indicate the presence of DMSO, which is the solvent that has been used to dissolve the solute, Dilantin, for the NMR instrument. The furthest peak at 174.7807 ppm represents the carbon from the amide carbonyl group (O=C-NH); the more the carbon is deshielded, the higher the peaks range will be. The peak at 155.9729 ppm indicates the carbon next to two amide groups (HN-C-NH). The range between 120-140 ppm typically represents carbons in aromatic rings. Total four peaks can be found in the data: peak at 139.8275 ppm, 128.4338 ppm, 127.9619 ppm, and 126.5161 ppm. They all represents the four distinct carbons in two benzyl rings. Lastly, the peak at 70.1653 ppm indicates the presence of quaternary carbon, which has four different R groups attached to it (C=O, two benzyl rings, and -NH). From this data, it is clear that there are no impurities in the synthesized product, since no other peaks were observed in the 13C NMR.From the analysis of both 13C and 1H NMR, and IR data, it is clear that the synthesis of Dilantin through condensation reaction between benzyl and urea, which involves benzylic rearrangement step, was successful. No trace of the starting material, benzyl, in the IR data suggests that the product was successfully synthesized. The presence of secondary amine group and secondary amide group at 3219.14 cm-1 and at 1669.93 cm-1, strongly suggests that the synthesized product is not benzil, and that it consists of two distinct functional groups containing nitrogen. In fact Dilantin has two types of secondary amine groups and two types of secondary amide groups as well. Where benzil only has two ketones and two aromatic benzyl rings attached on the side of the chain. From the 60MHz NMR, it was hard to conclude that the obtained data has a similar proton structure with the original, Dilantin. However, by using a higher resolution of NMR instrument, the 600MHz, it was clear that two small single peaks at 11.1964 ppm and 9.3963 ppm were observed under 1H 400MHz NMR data, which strongly suggest the presence of hydrogen attached to the secondary amine group. And a cluster of peaks at 7.3304-7.4112 ppm with integration value of ten hydrogens indicates the presence of aromatic benzyl ring in the sample. In summary, the 400MHz NMR data showed a similar proton structural patterns with the Dilantin. From the 13C 400MHz NMR, it was clear that the synthesized product contained seven distinct carbon groups: The amide carbonyl, the carbonyl with two N-H functional groups, the benzyl ring, and the quaternary carbon. Since the melting point of the synthesized product was very close to the pure compound, and no significant peaks indicating the impurities in the product were found from the IR and NMR, except for the presence of water in the solution, it is safe to conclude that the synthesized product is Dilantin.

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